This invention relates to transfer units for four-wheel vehicles and particularly to transfer units which enable four-wheel drive vehicles to be shifted between two-wheel drive and four-wheel drive, and low-gear and high-gear.
Four-wheel drive vehicles are highly desirable for off-road travel over rough terrain. However two-wheel drive vehicles are more desirable on normal hard, improved road surfaces. Therefore to satisfy the needs of the operator who drives on a variety of surfaces, vehicles have been produced that are capable of shifting between two-wheel drive and four-wheel drive. Traditionally, these types of vehicles could only be shifted between two-wheel drive and four-wheel drive when the vehicle was at a halt.
Recently, vehicles capable of shifting between two-wheel drive and four-wheel drive have been produced having transfer units that synchronize their front and rear output shafts before the actual shifting takes place. An example of such a transfer unit can be found in U.S. Pat. No. 4,555,846 to Cochran et al. The synchronizing apparatus in Cochran, however, is hard to repair and requires a plurality of parts that tend to wear out over time.
The capability to shift between low-gear and high-gear is also very desirable. This is especially so for four-wheel drive vehicles, which often encounter terrain that requires the use of low-gear at one point and high-gear at another point. In prior art vehicles having the capability to shift between low-gear and high-gear, such shifting could only be accomplished when the vehicle was at a halt. Stopping the vehicle in order to perform such a shift between low-gear and high-gear has proved to be very inconvenient, especially for the off-road racing enthusiast.